1. Field of the Invention
The present invention relates to a composition and a method for making a high volume reinforced aluminum (Al) composite by use of a dipping process, from powder mixture through such exothermic synthesis in a metal melt that reinforced particles are uniformly distributed while restraining the generation of pores.
2. Description of the Prior Art
Generally, conventional methods for making composite materials are classified into solid state processes using traditional powder metallurgical process; and liquid state processes, such as stir casting, squeeze casting, spray deposition, plasma process, DC casting, rheocasting, thixocasting and so on. However, the solid state processes suffer from the limitations in terms of economic efficiency and the liquid state processes have disadvantages that size of reinforcement is limited to tens of xcexcm or larger, and to amounts of 20% or lower within composite materials.
Up to now, the method for making high volume reinforced composite, other than powder methods, has been used as a method for impregnating metal into a preformed body comprising reinforcements under pressure or no pressure. But this method suffers from the disadvantages that wettability between the reinforcement and the melt is poor so that pore problems and the like occurs.
A dipping process is characterized in that reinforced particles themselves are formed in materials as one of in-situ synthesis process and thus the size of reinforcement may be controlled, thereby uniformly distributing very fine reinforced particles of 0.1-ones of xcexcm therein. Therefore the dipping process is possible to be called one of in-situ processes of composite materials. It is known that reinforced particles in the composite materials prepared by in-situ process have excellent interfacial properties. This is because the interfaces between matrix materials and newly formed reinforced particles are clean and continuous. Additionally, through the dipping process, final composite materials have the same shape as the preformed body, so that near net shaping can be realized.
From U.S. Pat. No. 4,710,348 (Brupbacher et al., Process for forming metal-ceramic composites), U.S. Pat. No. 5,336,291 (Nakami et al., Method of production of a metallic composite material incorporating metal carbide particles dispersed therein), and Japanese Patent Laid-Open Publication 63-83239 (Brupbacher et al., Process for forming metal-ceramic composites), it can be found that fine particles are dispersed in matrix structure through the in-situ synthesized process of composite materials.
However, in the conventional methods, Al composite having uniform particles cannot be obtained by a melt reaction, which is a exothermic reaction immediately following a synthesized process. As can be seen in FIG. 2a, reinforced particles of the composite prepared by the in-situ melt reaction process are heterogeneously distributed.
Conventionally, the inventors have tried to prepare a low volume fraction (10 vol % or less) composite by stirring of primary synthesized composite. In order to have homogeneously dispersed reinforced particles, primary synthesized composite is useful as a master alloy in the melt. And an extrusion process is introduced in order to obtain the uniformly redistributed reinforced particles in primarily prepared master alloy composite.
Accordingly, an object of the present invention for alleviating the problems as described above is to provide a composition for preparing a high volume reinforced Al composite from the powder mixture through such exothermic synthesis in a metal melt that reinforced particles are uniformly distributed while restraining the generation of pores.
Another object of the present invention is to provide a method for making a high volume reinforced Al composite from a preformed body formed by mixing said composition by use of a dipping process.
In accordance with an embodiment of the present invention, there is provided a composition for preparing a high volume reinforced Al composite by use of a dipping process, comprising 20-50 wt % of exothermic reaction-causing powders consisting of Ti and C or Ti and B, 20-60 wt % of exothermic reaction-controlling diluent powders, and 5-30 wt % of infiltration-aiding Al or Al alloy powders, said high volume reinforced Al composite being prepared from the powder mixture through such exothermic synthesis in a metal melt that reinforced particles are uniformly distributed while restraining the generation of pores.
Preferably, said exothermic reaction-controlling diluent powders are selected from the group consisting of TiC, TiB2, SiC, WC or mixtures thereof.
In accordance with another embodiment of the present invention, there is provided a method for preparing high volume reinforced Al composite by use of a dipping process, comprising the steps of: mixing 20-50 wt % of exothermic reaction-causing powders consisting of Ti and C or Ti and B, 20-60 wt % of exothermic reaction-controlling diluent powders, and 5-30 wt % of infiltration-aiding Al or Al alloy powders, then drying, to prepare mixture powders; preforming the mixture powders into a predetermined shape; fitting said preformed body in a reaction container, followed by dipping in an Al melt of 700-1,100xc2x0 C.; and separating said preformed body from the reaction container after removal from the Al melt, thereby yielding a high volume reinforced Al composite from the powder mixture through such exothermic synthesis in a metal melt that reinforced particles are uniformly distributed while restraining the generation of pores.
Preferably, said exothermic reaction-controlling diluent powders are selected from the group consisting of TiC, TiB2, SiC, WC or mixtures thereof.